This invention relates to an information storage medium used as an optical disk.
Various principles have already been known which are used for recording information on thin film (recording film) by irradiation of laser light. Among them, those which utilize the change of atomic arrangement, for example the phase change (also called phase transition or phase transformation), of the film material caused by laser light irradiation have an advantage in that since such changes are accompanied by virtually no deformation of the film, information storage media of double-side disk structure two disk members.
These information storage media are usually of a structure comprising a substrate and, thereon, a protective layer, a recording film of, for example, the GeSbTe type, a protective layer and a reflecting layer.
In this specification, the term xe2x80x9cphase changexe2x80x9d is used not only to represent the phase change between a crystalline state and an amorphous state but also to include the phase changes of melting (change to liquid phase) and recrystallization and phase change between a crystalline state and another crystalline state.
In rewritable optical disks, such as DVD-RAM, the recording tracks comprise a pre-formatted part provided with address pits, etc. serve for confirming the address, detecting the clock and synchronizing signal and a user data part which has grooves for tracking and conducts writing and reading information.
However, such optical disks have the following problem. Since the deformation caused by a stress acting between the stacked film and the substrate differs between the pre-formatted part and the user data part, the recording tracks are in a bent state relative to the pre-formatted part; resultantly, in a case where the light spot diameter represented by xcex/NA is 1.0-1.1 xcexcm and a high recording track density of a recording track width of not more than 0.8 xcexcm is used, when a push-pull tracking is applied to the grooves for tracking, the address data of the pre-formatted part cannot be read and, if the tracking offset is corrected so that the track of the light spot may come to the right position relative to the pre-formatted part, offset will occur in the recording region to cause erasion of a part of the data of the adjacent track. The reason for the difference in deformation between the pre-formatted part provided with address pits etc. and the user data part which conducts recording is considered that since the user data part has grooves for tracking, it is more apt to deform at the inclined part of the groove by applied force.
Another problem caused by the stress which acts between the stacked film and the substrate is that when many tracks are subjected to many times of rewriting by overwriting, the substrate surface is apt to expand and deform owing to heat evolved at the time of recording and the relaxation of the expansion takes long time and resultantly, the surface expansion is accumulated to become soft. Thus, owing to the stress exerted by the stacked film on the substrate, the grooves for tracking bend towards the direction of applied force by the stress. The bend is the larger as the position of the groove is the nearer to the center of the many-times recording region.
The object of this invention is to provide, overcoming the problems mentioned above, an information storage medium which can retain good and highly reliable write and read characteristics even when subjected to overwriting in a high recording density.
To solve the above-mentioned problems, two fundamental solving means are used for the information storage medium of this invention; that is, to reduce the stress acting between the stacked film and the substrate as much as possible and to reduce the increase of the substrate surface temperature during deposition of films as much as possible. Reducing the stress acting between the stacked film and the substrate is conducted by providing a stress-compensation layer. However, the substrate surface temperature rises during film formation and film attaches thereto in an expanded state; then when the substrate is cooled, the stress exerted by the substrate on the film is compression stress and the stress differs depending on the increase of the substrate temperature, so that the stress may possibly differ between at the start of production of the storage medium and during the continuous production. In such a case, the influence of the change of the substrate surface temperature can be made to be absorbed by controlling the film thickness of the stress-compensation layer.
According to this invention, there are provided an information recording medium and a method for manufacture thereof described below.
(1) An information storage medium which effects writing and reading by laser light which has a film containing 70 atomic % or more of at least one element selected from the group consisting of Cr, Ti, V Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb and Mo, said film having a thickness of 30 nm or more and having a pillar-like structure continuing from the lower face to the upper face of the film in at least 80% of the section of the film.
(2) An information storage medium which has at least two layers each containing 60 atomic % or more of metal at the more back side than the recording film when seen from the light incident side, one of the said layers containing 60 atomic % or more of at least one metal element having an atomic number of not less than 22 and not more than 47 and having a film thickness of 30 nm or more.
(3) The information storage medium described in (2) wherein the layer containing 60 atomic % or more of metal contain 60 atomic % or more of at least one metal element having an atomic number of not less than 22 and not more than 28 and have a film thickness of 30 nm or more.
(4) The information storage medium described in (2) above which have three above-mentioned layers containing 60 atomic % or more of at least one metal element.
(5) The information storage medium described in (2) above wherein the metal element having an atomic number of not less than 22 and not more than 47 is at least one of Ti and Cr.
(6) The information storage medium described in (2) above wherein, among the above-mentioned at least two layers each comprising metal as the main component, the layer nearest to the light incident side comprises Cr or Mo as the main component.
(7) The information storage medium described in (2) above wherein the layer comprising metal as the main component which contains 60 atomic % or more of at least one metal element having an atomic number of not less than 22 and not more than 47 and has a thickness of 30 nm or more is present on the more front side when seen from the light incident side, than the other layer(s) comprising metal as the main component.
(8) The information storage medium described in (2) above wherein the layer comprising metal as the main component which contains 60 atomic % or more of at least one metal element having an atomic number of not less than 22 and not more than 47 and has a film thickness of 30 nm or more is present on the more back side, when seen from the light incident side, than the other layer(s) comprising metal as the main component.
(9) The information storage medium described in (8) above wherein the layer(s) comprising metal as the main component other than the above-mentioned layer comprising metal as the main component which contains 60 atomic % or more of at least one metal element having an atomic number of not less than 22 and not more than 47 and has a film thickness of 30 nm or more contain(s) 70 atomic % or more of Al or Ag.
(10) The information storage medium described in (2) above wherein the layer between the at least two metal layers and recording film is at least one dielectric material layer and the whole thickness of the at least one dielectric material layer is not less than 10 nm and not more than 50 nm.
(11) The information storage medium described in (2) above wherein the layer containing 60 atomic % or more of at least one metal element having an atomic number of not less than 22 and not more than 47 has a film thickness of not less than 50 nm and not more than 150 nm.
(12) An information storage medium which comprises a substrate and, stacked thereon in the following successive order, at least a dielectric material layer having a thickness of not less than 100 nm and not more than 140 nm, a recording film having a thickness of not less than 5 nm and not more than 20 nm, a dielectric material layer having a thickness of not less than 10 nm and not more than 50 nm, a layer comprising at least one metal element as the main component and having a thickness of not less than 20 nm and not more than 70 nm, a layer containing 60 atomic % or more of at least one metal element having an atomic number of not less than 22 and not more than 47 and having a film thickness of not less than 50 nm and not more than 150 nm, and layer comprising at least one metal element as the main component and having a thickness of not less than 20 nm and not more than 200 nm.
(13) An information storage medium which comprises a substrate and, stacked thereon in the following successive order, at least a dielectric material layer having a thickness of not less than 100 nm and not more than 140 nm, a recording film having a thickness of not less than 5 nm and not more than 20 nm, a dielectric material layer having a thickness of not less than 10 nm and not more than 50 nm, a layer comprising at least one metal element as the main component and having a thickness of not less than 20 nm and not more than 70 nm, a layer comprising at least one metal element as the main component and having a thickness of not less than 20 nm and not more than 200 nm, and a layer containing 60 atomic % or more of at least one metal element having an atomic number of not less than 22 and not more than 47 and having a film thickness of not less than 50 nm and not more than 150 nm.
(14) The information storage medium described in (12) or (13) above wherein, among the at least two above-mentioned layers comprising at least one metal element as the main component, the layer of the side nearest to the light incident side comprises Cr or Mo as the main component.
(15) The information storage medium described in (12) or (13) above wherein the layer comprising at least one metal element as the main component and having a thickness of not less than 20 nm and not more than 200 nm contains 70 atomic % more of Al or Ag.
(16) The information storage medium described in (2) above wherein the recording film effects recording by phase exchange.
(17) The information storage medium described in (2) above wherein the substrate has a recording track pitch of not less than 0.3 xcexcm and not more than 0.7 xcexcm and has pit trains which represent address information, etc. at positions shifted from the track center.
(18) The information storage medium described in (8) above wherein the above-mentioned other layer(s) comprising metal as the main component comprise(s) Ag as the main component and the number of layers of the recording stacked film is 6.
(19) An information storage medium which effects writing and reading by laser light which has a layer containing 60 atomic % or more of at least one metal element having an atomic number of not less than 22 and not more than 47, said layer being a layer formed at an Ar flow rate of 120 SCCM or more.
(20) A method of manufacturing an information storage medium which effects writing and reading by laser light which method comprises forming a layer containing 60 atomic % or more of at least one metal element having an atomic number of not less than 22 and not more than 47 at an Ar flow rate of 120 SCCM or more.
(21). An information storage medium which has at least one layer containing 60 atomic % or more of at least one metal element having an atomic number of not less than 22 and not more than 47 and having a film thickness of 30 nm or more.
(22) The information storage medium described in (21) above wherein the above-mentioned layer containing 60 atomic % or more of a metal element having an atomic number of not less than 22 and not more than 47 is a layer of a Tixe2x80x94Cr or Vxe2x80x94Cr alloy which contain not less than 30 atomic % and not more than 85 atomic % of Cr, and not less-than 15 atomic % and not more than 70 atomic % of Ti or V.